Method of preparation of aromatic linear polyesters



Patented Apr. 22, 1952 METHOD OF PREPARATION OF AROMATIC LINEARPOLYESTERS Paul J. Flory, Ithaca, N; Y., and Frederick S. Leutner,Cuyahoga Falls, Ohio, assignors to Wingfoot Corporation, Akron, Ohio, acorporation of Delaware N Drawing. Application January 22, 1949, SerialNo. 72,256

Thisinvention relates to a novel method of preparing superpolyesterswhich are unusually well adapted to drawing fibers and which haveimproved heat stability. More specifically the invention relates topolyesters made by the condensation of terephthaloyl chloride orisophthaloyl chloride with tetramethylene glycol.

In copending application Serial No. 695,056, filed September 5, 1946,now abandoned, there is described and claimed a particular polymer,tetramethylene terephthalate, which has an unusually high melting pointand is therefore particularly useful in the preparation of desirablefibers. These fibers can be cold drawn to develop high tensile strengthand low residual elongation.

Copending application Serial No. 760,690, filed July 12, 1947, describesand claims tetramethylene isophthalate, another high melting polyestercapable of forming fibers.

Copending application Serial No. 683,990, filed July 16, 1946, nowPatent 2,589,688 issued March 18, 1952, describes and claims methods ofpreparing superpolyesters by an improved process involving the use ofcertain aromatic dibasic acid chlorides and glycols, whereby very highmolecular weight compositions may be obtained in relatively shortreaction periods. In this method, the polyesters are prepared bycondensing a glycol with a dibasic acid chloride with the eliminationofhydrogen chloride. While it is possible to prepare tetramethyleneterephthalate and tetramethylene isophthalate of very high molecularweight by this method, it has been found that, at the high temperaturesused to complete the re action, there is some tendency for unreactedglycol to decompose and for side reactions to take place with somediscoloration of the product. These effects may be reduced by efficientremoval of the hydrogen chloride from the reaction system but it isdifiicult to eliminate them entirely. The solution of this problem isone of the principal objects of the present invention. Other objectswill be apparent from the description of the invention hereinafter setforth.

It has been found that, in the condensation of tetramethylene glycolwith 'terephthaloyl chloride or isophthaloyl chloride, thedecompositionof the Claims. (Cl. 260-45) 'tetramethylene glycol and the undesiredside re- 2 actions may be minimized substantially by using a smallproportion of a higher molecular weight glycol which is more stableunder the rigorous conditions required to complete the condensation ofthe superpolyester. For example, tetramethylene glycol in an amountequal to from to 99 mol percent, and preferably to 98 mol percent, ofthe acid chloride is preliminarily reacted with the acid chloride andthe reaction is then completed with a higher molecular weight glycol inan amount approximately equal to the molecular excess of acid chlorideused in the first stage. The preferred practice utilizes a two to tenmol percent deficiency of tetramethylene glycol in the first stage ofthe reaction and subsequently the same molecular amount of the higherglycol to complete the condensation.

The first stage of the reaction is represented by the equation HO (CH2)tOH-l-CICORCOCl C1[CORCOO(CH2) 4OlnCORCOCl to give a low molecularweight polyester having terminal acid chloride radicals where n is awhole integer from 6 to 99 (and preferably 9 to 50) and --CORCO is aterephthaloyl or isophthaloyl radical. The second stage of thecondensation is represented by the equation giving the final highmolecular weight polyester with number average molecular weights in therange of 15,000-40,000, in which R is an aliphatic hydrocarbon,oxahydrocarbon or thiohydrocarborradical having more than four atoms inthe chain between the O-atoms, and m is a whole number less than 15 andpreferably between 10 and 2.

The higher glycols used in the second stage of the reaction are thealiphatic hydrocarbon, oxahydrocarbon and thiohydrocarbon glycols havingmore than four atoms in the connecting chain between the hydroxylgroups, including cyclo-aliphatic glycols. Straight chain glycols arepreferred and the polymethylene glycols are particularly useful.Representative examples are pentamethylene glycol, hexamethylene glycol,decamethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, di(betahydroxyethyl) sulfide (HO-C2H4SC2H4-OH),33-dihydroxy dipropyl sulfide of the reaction.

In accordance with this invention, superpolyesters are prepared bycharging an autoclave, preferably of glass or lined with glass, with therequired proportions of acid chloride and tetramethylene glycol, anexcess of the acid chloride being used. In order to prevent thedecomposition of the polymer at the reaction temperatures, it isnecessary to sweep out the reaction vessel with a stream of nitrogen, orother inert gas, prior to initiating the reaction. Such treatmentcompletely eliminates all oxygen which may have been initially presentin the reaction vessel. It is also desirable to continue flowing thestream of inert gas through the vessel during the course of the reactionfor the purpose of maintaining the,

reaction vessel free of gaseous oxygen and for eliminating the hydrogenchloride generated by the condensation reaction. The reaction vessel isalso provided with a suitable means for applying a vacuum to thereaction mass for removing bubbles of gas from the viscous polymer.After a short preliminary heating period at temperatures above themelting point of the reaction mixture, followed by a further shortheating period at 200-250 C., a low molecular weight polymer isobtained.

The course of the reaction may be followed by periodically measuring theviscosity of the reaction mass by the use of a glass tube insertedthrough the Walls of the reaction vessel and adapted to be immersed inthe molten reaction mass. The method of measuring the melt viscosity bywhich the course of the reaction is followed is fully described in theJournal of the American Chemical Society, volume 62, page 1057.

The second step of the reaction involves the addition of a proportion ofa glycol having a chain of more than four atoms between the two hydroxylgroups, which proportion is approxi- 'mately equivalent to the molecularexcess of acid chloride used in the first step of the reaction. In theevent that any of the acid chloride or tetra methylene glycol is lostduring the first step of the reaction, it will be necessary to add moreor less of the higher glycol in order that there may be present in thefinal reaction mass as nearly equimolecular proportions as possible ofthe dibasic acid units and total glycol units.

There are several methods which may be used to assure the presence ofequivalent proportions of reactants in the vessel during the final step7 It may be done by trial-anderror method whereby, over the course ofmany .preparations, the proportion of added material required to producethe maximum viscosity is learned. The same objective may be obtained byincrement addition of the higher molecular weight glycol, by whichmethod small proportions of the higher glycol are added and measurementsof the melt viscosity made subsequent to the addition of each increment,the reaction being completed when a desirable high molecular weightpolyester is found to exist.

The preferred method of estimating the proportion of higher glycolrequired to complete the reaction involves the use of a standardizedmethed for performing the first step of the reaction and estimating therequired proportion of additional glycol from the melt viscosity of themass at the end of the first stage of reaction. This latter methodrequires the use of a plotted curve showing the relationship of meltviscosity' to excess of acid chloride, which curve is prepared after. aseries of-carefully controlled ex-- periments involving accuratelymeasured proportions of reagents.

According to an alternate method which may be used in the practice ofthis invention, the molten acid chloride is charged into the reactionvessel and the tetramethylene glycol is then fed into the mass of moltenacid chloride in small portions or continuously until the intermediatepolymer of desired viscosity is obtained. This method involves the useof apparatus provided with a glycol inlet at the bottom of theautoclave, which may be the same inlet used to deliver the inert gas tothe reaction vessel. In accordance with this method the reaction vesselis flushed out with inert gas and charged with acid chloride. Thereaction is initiated by introducing tetramethylene glycol into the acidchloride through the gas inlet tube While maintaining a continuous orintermittent flow of the inert gas into the vessel. The temperature isgradually raised so as to maintain the reactants in molten condition.When the temperature has reached a maximum of 230-250 C. the reactionmass soon reaches a maximum viscosity, the value of which will dependupon the extent of the acid chloride excess, the smaller excessproducing the more viscous product. The excess of acid chloride at thistime may be estimated by any of the methods described in the precedingparagraphs, and this required amount of higher glycol is carefully addedthrough the inlet tube to secure a polyester having a melt viscositybetween 1000 and 5000 poises.

The first stage of the reaction is preferably started at a relativelylow temperature, which is gradually increased as the reaction proceedsin order to keep the reaction mass melted. The completion of this firststage is facilitated by finally heating for a short time at atemperature of about 200-250" C. The second stage of the reaction, usingthe higher glycol, is carried out entirely at the higher temperaturesrequired to keep the reaction mass melted, for example, at about 240-255C. The time required for the second stage will, of course, vary with themolecular weight desired in the product but will usually be about one totwo hours.

The periodic determination of the melt viscosity, used in following theprogress of the reaction, may also be used in estimating the molecularweight of the polymer. The average molecular weight M is related to themelt viscosity in accordance with the empirical equation log N=A+BMwherein N is the melt viscosity in poises and A and B are constantsdepending upon the particular reagents being used. These constants canbe established by measuring the ether. sharply trom fill fi to 84.5? C.The isophthaloyl :chlorlde-can-bepurified by successive crystalviscosityof several polymers of known molecular weights.

It is important to employ pure reactants in either method of preparingthe polyesters. The tetramethylene glycol can be purified satisfactorilyby crystallization from a 2 :3 mixture of dry acetone and dry ether. Thefreezing point is a good criterion of the purity of the glycol. Thefreezing point of the tetramethylene glycol should be at least to beassured of its purity (although a lower freezing point can be toleratedwith certain types of impurities), and preferably it should be in therange 193 to 202 C. The terephthaloyl chloride can be purifiedconveniently by re-crystallizing it from dry petroleum ts. purity. iswell assured if it melts lization of the distilled acid chloride fromdry hexane or petroleum ether. Its melting point should be at leastLi-46 C. Both the acid chloride and the glycol should becarefullyprotected from moisture.

The condensation superpolymers of tetramethylene terephthalate andtetramethylene isophthalate, modified in accordance with this inventionby the completion of the reaction with a higher molecular weight glycol,are valuable sources of synthetic textile fibers which can be made byspinning or extruding the liquefied polymer through suitable dies. Theextruded filaments are then solidified. The filaments so prepared may bestrengthened and rendered less thermoplastic by subjecting them tostretching action which causes a molecular orientation. Such orientationof the fibers by stretching is conducted at temperatures below thesoftening points and is usually called cold-drawing.

The oriented or cold-drawn fibers may be twisted into thread or yarn, orused in singlefilament form, in the preparation of textile fabrice. Thefilaments may also be used as bristles in the fabrication of varioustypes of brushes.

Further illustrative details of the preparation of the new polyestersare set forth in the following examples:

Example 1 A glass reaction vessel provided with an adjustable glassinlet tube and a stirring device was charged with 46.1 parts by weightof pure terephthaloyl chloride. While vigorously stirring theterephthaloyl chloride, 19.4 parts by weight of pure tetramethyleneglycol were added gradually over a period of 75 minutes. During thereaction a continuous stream of nitrogen was introduced into thereaction mass by means of the glass tube, the end of which was immersedin the molten reactants. The temperature at the outset was that requiredto melt the terephthaloyl chloride and the temperature was raisedgradually so as to maintain the reaction mass in molten condition. Afterall of the glycol had been added the temperature was 237 C., whichtemperature was maintained for an additional 45 minutes while the vesselwas evacuated to remove gas bubbles and dissolved hydrogen chloride. Atthis point the melt viscosity was 58 poises, corresponding to themolecular weight of 7500. A portion of decamethylene glycol (1.071 partsby weight) equivalent to the 2.7 molar percent excess of terephthaloylchloride (determined empirically from the viscosity) was added in threeseparate portions while continuously stirring the reaction mass. Afterheating the reaction mass for two hours it was found to have a viscosityof 2500 poises and a molecular weight of 22,000. On cooling, the polymercrystallized to a white solid having a melting point of 222-223.5 0.,which was less than 4 C. below the melting point of a tetramethyleneterephthalate unmodified by the addition of decamethylene glycol.

Emamplc 2 Using the apparatus and procedure set forth in Example 1, 16.0parts by weight of tetramethylene glycol and 37.5 parts by weight ofterephthaloyl chloride were reacted for 95 minutes while graduallyincreasing temperatures from 82 C. to 218 C., the glycol being addedslowly as in Example 1. The reaction mixture was then heated for 40minutes at 237 C. with the application of vacuum to remove gaseousreaction products. At this time the melt viscosity was 2.7 poises,corresponding to a molecular weight of about 1300. Then 2525 parts myweight of decamethylene glycol, corresponding to 7.8 molar percentexcess of terephthaloyl chloride, indicated by the viscosity, were addedover a period of 210 minutes. After fur ther heating for90 minutes, thepolymer was found to have a viscosity of 1500 poises, corresponding to amolecular weight of 20,000. The resulting polymer was a whitecrystalline solid having a melting point of 214.5-217" C. It was drawninto excellent fibers capable of being cold drafted.

Isophthaloyl chloride and other glycols than decamethylene glycol may beused similarly.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modications may be madetherein without departing from the spirit or scope of the invention.

We claim:

1. A method of preparing a superpolyester which comprises mixing andheating a dibasic acid chloride selected from the group consisting ofterephthaloyl chloride and isophthaloyl chloride with from 85 to 99percent of an equivalent proportion of tetramethylene glycol at atemperature above the melting point of the reaction mass until a viscouspolyester is formed, adding to this polyester, in an amountapproximately equivalent to the excess of acid chloride, a glycolselected from the group consisting of aliphatic hydrocarbon,oxahydrocarbon and thiahydrocarbon glycols having more than four atomsin the molecule chain between the hydroxyl groups, and continuing theheating at temperatures above the melting point of the reaction massuntil a high molecular weight superpolyester is formed.

2. A method of producing a superpolyester which comprises heatingterephthaloyl chloride with from 85 to 99 percent of an equivalentproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with a different glycol in an amountapproximately equivalent to the excess of terephthaloyl chloride, saidlatter glycol being selected from the group consisting of aliphatichydrocarbon, oxahydroca-rbon and thiahydrocarbon glycols having morethan four atoms in the molecule chain between the hydroxyl groups, toform a superpolyester.

3. A method of producing a superpolyester which comprises heatingisophthaloyl chloride with from 85 to 99 percent of an equivalentproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with a different glycol in an amountapproximately equivalent to the excess of isophthaloyl chloride, saidlatter glycol being selected from the group consisting of aliphatichydrocarbon, oxahydrocarbon and thiahydrocarbon glycols having more thanfour atoms in the molecule chain between the hydroxyl groups, to form asuperpolyester.

4. A method of producing a superpolyester which comprises heatingterephthaloyl chloride with from 85 to 99 percent of an equivalentproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with decamethylene glycol in cess ofterephthaloyl chloride to form a superpolyester.

5. A method of producing a superpolyester which comprises heatingisophthaloyl chloride with from 85 to 99 percent of an equimolecularproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with decamethylene glycol in an amountapproximately equivalent to the molecular excess of isophthaloylchloride to form a superpolyester.

6. A method of producing a superpolyester which comprises heatingterephthaloyl chloride with from 90 to 98 percent of an equimolecularproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with a difierentglycol in an amount approximatelyequivalent to the molecular excess of terephthaloyl chloride, saidlatter glycol being selected from the group consisting of aliphatichydrocarbon, oxahydrocarbon and thiahydrocarbon glycols having more thanfour atoms in the molecule chain between the hydroxyl groups, to form asuperpolyester.

7. A method of producing a superpolyester which comprises heatingisophthaloyl chloride with from 90 to 98 percent of an equimolecularproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with a different glycol in an amountapproximately equivalent to the molecular excess of isophthaloylchloride, said latter glycol being selected from the group consisting ofaliphatic hydrocarbon, oxahydrocarbon and thiahydrocarbon glycols havingmore than four atoms in the molecule chain between the hydroxyl groups,to form a superpolyester.

8. A method of producing a superpolyester which comprises heatingvterephthaloyl chloride with from 85 to 99 percent of an equivalentproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with hexamethylene glycol in an amountapproximately equivalent to the excess of terephthaloyl chloride to forma superpolyester.

9. A method of producing a superpolyester which comprises heatingisophthaloyl chloride with from to 99 percent of an equivalentproportion of tetramethylene glycol to form a linear polyester havingterminal acid chloride radicals and then heating said linear polyester,in a molten condition, with hexamethylene glycol in an amountapproximately equivalent to the excess of isophthaloyl chloride to forma superpolyester. 7

10. A method of producing a superpolyester which comprises heating adibasic acid chloride selected from the group consisting ofterephthaloyl chloride and isophthaloyl chloride with from 85 to 99percent of an equivalent proportion of tetramethylene glycol to form alinear polyester having terminal acid chloride radicals and then heatingsaid linear polyester, in a molten condition, with pentamethylene glycolin an amount approximately equivalent to the excess of acid chloride toform a superpolyester.

PAUL J. FLO'RY. FREDERICK S. LEUTNE R.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,437,046 Rothrock et a1 Mar. 2,1948 2,465,319 Whinfield et al Mar. 22, 1949 FOREIGN PATENTS NumberCountry Date 63,874 Denmark Aug. 27, 1945

1. A METHOD OF PREPARING A SUPERPOLYESTER WHICH COMPRISES MIXING ANDHEATING A DIBASIC ACID CHLORIDE SELECTED FROM THE GROUP CONSISTING OFTEREPHTHALOYL CHLORIDE AND ISOPTHALOYL CHLORIDE WITH FROM 85 TO 99PERCENT OF AN EQUIVALENT PROPORTION OF TETRAMETHYLENE GLYCOL AT ATEMPERATURE ABOVE THE MELTING POINT OF THE REACTION MASS UNTIL A VISCOUSPOLYESTER IS FORMED, ADDING TO THIS POLYESTER, IN AN AMOUNTAPPROXIMATELY EQUIVALENT TO THE EXCESS OF ACID CHLORIDE, A GLYCOLSELECTED FROM THE GROUP CONSISTING OF ALIPHATIC HYDROCARBON,OXAHYDROCARBON AND THIAHYDROCARBON GLYCOLS HAVING MORE THAN FOUR ATOMSIN THE MOLECULE CHAIN BETWEEN THE HYDROXYL GROUPS, AND CONTINUING THEHEATING AT TEMPERATURES ABOVE THE MELTING POINT OF THE REACTION MASSUNTIL A HIGH MOLECULAR WEIGHT SUPERPOLYESTER IS FORMED